1. Field of the Invention
The present disclosure relates to a backlight unit for a head-up display apparatus.
2. Discussion of Related Art
A display apparatus for a vehicle effectively transmits information to a driver while the vehicle is traveling. A representative example of the display apparatus for a vehicle is a head-up display apparatus.
Such a head-up display apparatus includes a backlight unit for collecting light emitted from a light-emitting diode (LED) source and effectively transmitting the collected light to a panel.
FIG. 1A and FIG. 1B are a diagram for describing a configuration of a backlight unit. FIG. 2A and FIG. 2B are diagrams for describing a problem of a backlight unit according to a related art.
Referring to FIG. 1A and FIG. 1B, the backlight unit may employ a single LED or a plurality of LEDs according to a brightness requirement of a head-up display apparatus. At this point, a method for collecting light from an LED generally includes a lens method, shown in FIG. 1A and a reflector method, shown in FIG. 1B.
A backlight unit employing the lens method shown in FIG. 1A is configured with a light source 11 and a lens 13. A backlight unit employing the reflector method shown in FIG. 1B is configured with a light source 11′ and a reflective reflector 13′.
In a general structure of such a backlight unit, a normal line including the center point of a light emitting surface of the LED is defined as an optical axis of a light source, and the optical axis of the light source and an optical axis of an optical component for collecting light are configured to coincide with each other.
In this case, however, when the optical axis is disposed at the center of an eyebox a as shown in FIG. 2A, a problem in brightness uniformity does not occur, however a phenomenon in which brightness uniformity is degraded does occur as the optical axis moves toward a lateral surface inside the eyebox a shown in FIG. 2B.
When a scattering angle of a diffuser is increased to compensate for such a problem, a problem in that uniformity is improved but brightness is degraded occurs.
In this regard, a head-up display apparatus for projecting a display image on a projection member is disclosed in Japanese Patent Application Publication No. 2010-76666 (entitled, Head-Up Display Apparatus).